A conventional heater used in an aquarium as shown in FIG. 1 includes: a glass tube 1 having a heating coil 11 provided in a lower portion of the tube placed in the water of the aquarium, a thermo-sensitive resistor R1 and a heating indicator lamp 111 formed in the tube 1, a controller 2 having a thermostat 20 provided in a casing 200 having a variable-resistance adjusting knob VR1 rotatably formed on the casing 200 for setting a warm temperature of the thermostat 20, and a power source PS for powering the heater connected to the tube 1 through an adapter 120 formed on a cap 12 sealing the glass tube 1. The heater may serve for keeping a constant warm temperature in an aquarium for raising fishes.
However, such a conventional aquarium heater has the following drawbacks:
1. The thermostat 20 is provided in the casing 200 of controller 2 to occupy a large space, influencing the installation of other equipments such as light, filter, and air blower required for an aquarium and also spoiling their esthetic appearance.
2. The thermo-sensitive resistor R1 is provided in the glass tube 1 for sensing water temperature for activating the heating coil 11 as controlled by the thermostat 20. However, the resistor R1 is very near the heating coil 11 which is also provided in the glass tube 1 so that the resistor R1 may sense an incorrect signal of water temperature as thermally influenced by the heating coil 11 to falsely and unexpectedly switch off the heating operation of the coil 11 when heating is required.
3. An electric circuit for controlling and heating the aquarium is not provided with additional safety device so that once the controller 2 is out of order, the heating coil 11 will not be switched off, thereby continuously increasing water temperature and possibly killing fishes.
The present inventor has found the drawbacks of the conventional aquarium heater and invented the present aquarium safety heater.